Airflow baffle for commercial truck fuel efficiency improvements

ABSTRACT

An aerodynamic drag reduction device for use on an over-the-road cargo vehicle. The vehicle has a prismatically shaped cargo area, which includes a rear face of the cargo area substantially perpendicular to the direction of travel. The device comprises a plurality of resilient prongs arranged along a rear edge of the vehicle body, extending from a respective fixed end secured to the vehicle body rearward in a flow-wise direction beyond the rear edge of the vehicle body to a respective free end. Each prong is separated from an adjacent prong in the plurality, and each is flexible to permit deflection, under the influence of airflow over the vehicle at a predetermined speed, above and below a first plane defined by the surface of the vehicle to which the plurality of prongs is secured. Each prong is further resistant to deflecting in a direction parallel to the first plane.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates to the field of transportationaerodynamics. More specifically, disclosed is an apparatus to improvethe aerodynamic and fuel efficiency of an over-the-road cargo vehicle.

2. Brief Discussion of Related Art

The predominant mode of transportation for commercial goods throughoutthe United States, the developed world and elsewhere is cargo truck,among these including a tractor-trailer truck. For this mode oftransportation, fuel represents the largest single cost component.Therefore, any measureable improvement in fuel efficiency of suchvehicles is worthwhile.

In particular, in the developed world, where tractor-trailer truckstravel long distances of well-developed highways at a generally highspeed, aerodynamic drag represents a major source of inefficiency. Onesource of such aerodynamic inefficiency is the geometry of the truck,which is essentially an elongated rectangular prism. In particular, theairflow properties over the trailing edge of the trailer create a largetrailing negative pressure vortex, which greatly contributes to drag.

One recent technology to improve aerodynamic efficiency is colloquiallycalled a “boat tail”. A boat tail is an attachment to the rear end ofthe trailer which acts as a fairing to gradually reduce thecross-sectional area of the trailer, and thus reduce the size andintensity of the trailing vortex and its associated drag. Oneinvestigation by the Platform for Aerodynamic Road Transport (PART), aresearch affiliate of the Delft University of Technology, Netherlands,suggests a boat tail can contribute a 4.5% improvement in fuelefficiency.

However, a boat tail as it is currently practiced has a practical sizelimit that still necessitates an abrupt geometry change at its trailingedge. Furthermore, a trailer is accessed via doors at its rear. Any sortof boat tail impedes access to such doors. For many such tractor/trailertrucks the container itself is transferable in order to be used byintermodal transportation (i.e., train, or cargo ship). In thosecircumstances, the aerodynamics are either substantially different (e.g.rail), or not even a concern (i.e., container ship). In such cases, theinviolable requirement is that the container keep its standardized sizeand shape, to enable its intermodal transfer. Permanent alterations tothe shape of the trailer to improve efficiency are therefore impossible,to say nothing of the cost-effectiveness in construction of a boxtrailer. Even an aerodynamically effective successful boat tail shouldtherefore be temporary, removable or interchangeable for most practicaleffect.

Furthermore, in loading or unloading, a road-use trailer is mostcommonly backed up to an elevated loading dock. Attempts to deal withthis problem include making the boat tail inflatable, or foldable.Still, a boat tail remains an operational obstacle to loading andunloading.

Therefore, the present state of the art is lacking. Other solutions inplace of or in addition to a boat tail may yield even better aerodynamicresults and/or greater operational advantages.

SUMMARY

In order to overcome these and other weaknesses, drawbacks, anddeficiencies in the known art, provided according to the presentdisclosure is an aerodynamic drag reduction device for use on anover-the-road cargo vehicle, the vehicle having a prismatically shapedcargo area, including a rear face of the cargo area substantiallyperpendicular to the direction of travel. The device includes aplurality of resilient prongs arranged along a rear edge of the vehiclebody, each of the prongs extending from a respective fixed end securedto the vehicle body rearward in a flow-wise direction beyond the rearedge of the vehicle body to a respective free end. Each prong isseparated from an adjacent prong in the plurality. Each prong is furtherflexible to permit deflection of the free end above and below a firstplane defined by the surface of the vehicle to which the plurality ofprongs is secured. Such deflection is caused by the properties of theairflow over the vehicle at a predetermined speed. Each prong is furtherresistant to deflecting in a direction parallel to the first plane.

Alternately or additionally, a shaft of each prong has a perpendicularcross section with an area moment of inertia that is lowest around aneutral axis of the cross section that is substantially parallel to thefirst plane.

Optionally, each prong may include a composite construction of two ormore material sections, each material having a different modulus ofelasticity. Each prong may optionally include a vulcanized rubbermaterial in some embodiments. In certain embodiments, each prong has asubstantially uniform cross-section. In others, each prong has a taperedcross-section, in height or width, or both. For certain embodiments ofthe present disclosure, each prong has radiused corners at itsrespective connection to the space separating it from an adjacent prong.

Further described according to the present disclosure, optionally theplurality of prongs are secured to the vehicle with the capability to berepositioned from a deployed position having the free ends extendedbeyond a rear edge of the vehicle body, to a retracted position havingthe free end nearer to or forward of the rear edge of the vehicle body.In some cases, the device is slideable in a flow-wise direction toreposition the prongs.

In other embodiments, the device is secured to a rotating frame memberwhich is operative to be rotated between the deployed position and aretracted position. For certain rotatable deployed embodiments, thedevice is itself rotatable on the rotating frame member to maintain anorientation of the prongs in a rearward extending direction. Optionally,the rotating frame member may be securable in one of the deployed or theretracted positions.

BRIEF DESCRIPTION OF THE FIGURES

These and other embodiments of the present disclosure will becomeapparent from the following detailed description read in connection withthe accompanying drawings, wherein

FIG. 1 illustrates a generally conventional tractor-trailer cargo truck,having added thereto a drag-reducing airflow baffle according to thepresent disclosure;

FIG. 2 illustrates a detailed view of the upper rear portion of thecargo truck indicated by circle 2 in FIG. 1;

FIG. 3 illustrates a drag-reducing airflow baffle according to a firstembodiment of the present disclosure;

FIG. 4 illustrates a cross-section view of one baffle prong taken alongline 4-4 of FIG. 3;

FIG. 5 illustrates a drag-reducing airflow baffle according to a secondembodiment of the present disclosure;

FIG. 6 illustrates a cross-section view of one baffle prong taken alongline 6-6 of FIG. 5;

FIG. 7 illustrates on embodiment of a baffle-retracting scheme accordingto the present disclosure;

FIG. 8A illustrates a second embodiment of a baffle-retracting schemeaccording to the present disclosure, having the baffle retracted;

FIG. 8B illustrates the second embodiment of a baffle-retracting schemeaccording to the present disclosure, having the baffle in anintermediate position; and

FIG. 8C illustrates the second embodiment of a baffle-retracting schemeaccording to the present disclosure, having the baffle deployed.

DETAILED DESCRIPTION

Referring now to FIG. 1, illustrated is a tractor-trailer truck,generally 100, the features of which are largely conventional. While atractor-trailer 100 is described, the present disclosure will be seen asapplicable to any cargo vehicle with a prismatic shape of the cargosection, for example and without limitation, a box truck, a car-pulledtrailer, or the like. The tractor cab 110 includes a cabin for theoperators and an engine (not shown) to power itself and pull one or moreattached trailers 120. Airflow streamlines 130, 140 depict the flow ofair over the truck 100 at generally highway speeds, e.g., 60 miles perhour (MPH) or roughly 95 kilometers per hour (kM/h).

Attached to the rear of the trailer 120 is an airflow baffle 150.Airflow baffle 150 is visible vertically in FIG. 1, being attached to anear side on the trailer 120. Not visible in FIG. 1, is a further baffle150 that can be mounted vertically at the rear of trailer 120 along anopposite side facing away from the viewer. Another baffle 150 may bemounted horizontally across a top of the trailer 120, again extendingrearward analogous to the baffle 150 shown in FIG. 1.

The prismatic geometry of a standard trailer 120, in particular theabrupt change of shape at its trailing end, creates a large low pressurevortex immediately behind the trailer 120 when there is airflow over thetrailer 120, for example at highway speed. This low pressure vortex is alarge contributor to aerodynamic drag. In order to minimize the dragassociated with this trailing vortex it is advantageous to control orinfluence the flow of air into the space immediately behind the trailer.

With reference to FIG. 2, the upper rear end of the trailer 120 isdepicted without any baffle 150 attached thereto to illustrate thetypical airflow behavior. Experimental observation and computationalfluid dynamics flow simulation indicates that, at the abrupt right-angletrailing edge of the trailer 120 the flow induced is characterized by adynamic sinusoidal or wavelike pattern, generally indicated bystreamlines 202. This flow pattern is dynamic in the sense that the wavepattern shifts with a sinusoidal or wavelike characteristic as flow overthe trailer 120 separates from the trailer 120 and mixes with fluidbehind the trailer 120. This sinusoidal or wavelike flow pattern isaccompanied by mixing vortices 204. In order to delay the separation ofairflow from the trailer, and thus reduce drag formed by the separation,it would be beneficial if the surface of the trailer could be made tomove with the sinusoidal or wavelike flow pattern. In this manner, themixing of airflow over the trailer 120 into the trailing vortex would becontrolled, and distributed over a greater volume as the separation isextended behind the trailer 120. The intensity of the pressuredifferential behind the trailer 120 is therefore reduced, and with itthe accompanying drag.

Referring Now to FIG. 3, the flow baffle 150 provides prongs 152 thatare positioned to extend in the flow-wise direction, generally alignedwith a longitudinal axis of the trailer 120, which can be seen asextending in parallel to the x-axis direction as depicted in FIG. 1.Prongs 152 are separated from one another by spaces 154, which spacesallow respective free ends 156 of individual prongs 152 to moveindependently of one another. Opposite the free end 156 of each prong152 is a fixed end 158. The free end 156 of each prong 152 is connectedto a respective fixed end 158 by a shaft 162. Fixed ends 158 may besecured to one another and the baffle 150 in general by a common spine160. The space between prongs 152 at the spine 160 may be provided withindividual or blended fillets 164, in order to avoid stressconcentration. Alternately or additionally, the fixed ends 158 may besecured to the trailer 120 itself.

In a very particular embodiment, the prongs 152 are approximately 2inches in width, between about 0.5 to 1 inches in thickness, and up toabout 14 inches in length. Spacing 154 between the prongs 152 can beabout 1 inch. However, these dimensions are offered as an example only,and should not be taken to limit the scope of the disclosure. These andother relevant dimensions are left to the particular application asdetermined by those skilled in the art taken in light of Applicant'spresent disclosure.

The baffle 150 is secured to the trailer 120 to permit the shaft 162 ofeach prong 152 to extend, in whole or in part, rearward beyond atrailing edge of the trailer 120. Moreover, the prongs 152 areresiliently constructed to permit their flexure above or below a planedefined by a side surface of the trailer 120 to which they are secured.The degree of resiliency and flexure will be subject to adjustmentaccording to the individual circumstances. Among the factors to beconsidered are the dimensions of the trailer 120, the design operatingspeed at which drag is to be minimized, resultant Reynolds number forthe particular flow, etc. As a first order approximation, prongs 152constructed of vulcanized rubber display what is considered to be anadequate degree of resiliency for the present application.

Composite makeup may be employed as well, for example the prongs havinga core of a harder material, ductile metals, resilient plastics or thelike, with additional flexibility afforded by a covering of moreflexible material over this core. Optionally, some or all of the baffle150 in gross may have the same composite construction as the prongs 152.The cross-sectional view of the prong 152 indicates a compositeconstruction, including a core 168 having an alternate material, inparticular a differing modulus of elasticity, as the material comprisingthe remainder of the prong 152. The cross-sectional shape of the core168 need not necessarily conform to that of the prong 152 as a whole.Moreover, the length of the core 168 may optionally be less than that ofthe prong 152. The core 168 may have a uniform cross-section, or it maytaper or otherwise change in cross-sectional area without regard to theshape of the prong 152.

The precise cross-sectional dimension of the prongs 152 will also affectthe flexibility of the prongs 152. Generally speaking, it is considereddesirable that the prongs have flexibility to deflect above or below thedesignated mounting plane, but only limited flexibility laterally withinthe mounting plane. To this end, the cross-sectional geometry shouldexhibit a greater area moment of inertia (alternately called secondmoment of area) around any axis extending out of the mounting plane ascompared with the area moment of inertia around any axis lying in orparallel to the mounting plane. As a result, the prongs will resistflexing around any axis having a higher area moment of inertia, whichcan be by design an axis lying parallel to the mounting plane.

As an example only, and with reference to FIG. 4, a cross-section viewof the prong 152 taken along section line 4-4 in FIG. 3, illustratesthat the prong 152, and particularly its shaft 162, have a lowest areamoment of inertia around the horizontal axis 165 passing through thecenter of the shaft 162. In certain embodiments, the corners 166 of theshaft 162 may be rounded to avoid stress concentrations and improvedurability in service.

Referring now to FIG. 5, illustrated is an alternate embodiment of abaffle, generally 250. A full description of the features common withthe foregoing embodiment of FIGS. 3-4 will be apparent to those skilledin the art, and the following description will highlight the differencestherewith. Baffle 250 has prongs 252 separated from one another byspaces 254. The shaft 262 of each prong 252 is tapered in its width atit extends rearwardly in a flow-wise direction, with a tape r angle 270defined by θ. FIG. 6 is a cross-section view of the prong 252 takenalong section line 6-6 in FIG. 5. Here again, the prong 252, andparticularly its shaft 262, have a lowest moment of inertia around thehorizontal axis 264 passing through the center of the shaft 262.Accordingly, they will tend to flex above or below the mounting plane,and resist lateral deflection within or parallel to the mounting plane.Alternately or additionally, the prong cross-section may be tapered inheight to influence the propensity of the prong to defect vertically (asviewed in FIG. 4 or 6 only; the prepared axis of deflection willgenerally be laterally for baffles installed on a side surface of thetrailer) rather than horizontally.

The cross-sectional view of the prong 252 indicates a compositeconstruction, including a core 268 having an alternate material, inparticular a differing modulus of elasticity, as the material comprisingthe remainder of the prong 252. Notably, the cross-sectional shape ofthe core 268 need not necessarily conform to that of the prong 252 as awhole. Moreover, the length of the core 268 may optionally be less thanthat of the prong 252. The core 268 may have a uniform cross-section, orit may taper or otherwise change in cross-sectional area without regardto the shape of the prong 252.

A trailer 120 fitted with one or more baffles 150, 250, obtains itsbenefit of drag reduction in transit at highway speeds. However, such atrailer 120 should preferably be compatible with the existing truckinginfrastructure in other phases of operation, namely loading andunloading. Loading and unloading of the trailer 120 is most commonlyaccomplished by one or more doors at the rear face 122 of the trailer120. Moreover, for this purpose, a raised loading dock (not shown) iscommonly provided level with the bottom 125 of the trailer 120. Theheight of such a dock is generally standardized. In order for thetrailer 120 to be backed into position adjacent to such a loading dockfor loading and unloading, it is desirable that the baffles 150 or 250be retractable such that they do not extend beyond the rear face 122 ofthe trailer 120.

Referring now to FIG. 7, illustrated is a mounting arrangement where thebaffle 150 is mounted to the trailer 120 in a manner that permits thebaffle 150 to be shifted along a longitudinal axis of the trailer 120.In particular, a plurality of pegs 180 is provided on the trailer 120,which fit respectively into one or more of in spaces 154 betweenadjacent prongs 152. Accordingly, the baffle 150 can slidelongitudinally along the trailer 120 from a position with free ends 156extended beyond the rear face 122 of the trailer 120, as shown in FIG.7, to a retracted position having the free ends 156 longitudinallyforward of the trailer rear face 122 (not shown). Moreover, the baffle150 may be adapted to be secured in one of several intermediatepositions as well. With the baffle 150 retracted, it does not impact norinterfere with the trailer 120 backing into to a loading dock, noraccess to the trailer 120 from the same. The baffle 150 may be securedin the extended, retracted, or any intermediate position by any numberof conventional means known in the art.

FIGS. 8A-8C illustrate an alternate mounting embodiment for baffles 150.In this embodiment, one or more baffles 150 are mounted to a pivotingframe 310. The pivoting frame is mounted to the trailer by a pluralityof mounts 312. A handle 314 is attached to the frame 310 to allow a userto pivot the frame 310 between retracted and deployed positions. One ormore handle latches 316, 318 are provided to hold the handle 314, andthereby the frame 310, in either the retracted or extended positions,respectively.

Baffles 150 are carried by the frame 310 on arms 320, such that arotation of the frame 310 from its retracted position illustrated inFIG. 8A, to an intermediate position illustrated in FIG. 8B, places thebaffles 150 with the fixed ends 158 in proximity to the rear face 122 ofthe trailer 120. From this intermediate position of FIG. 8B, in thisparticular embodiment, the baffles 150 may be mounted to the arms 320 ina pivotal manner, such that the baffles 150 are rotated into anoperating position illustrated in FIG. 8C, having the free ends 156 ofthe prongs 152 extending rearward beyond the rear face 122 of thetrailer 120. Thus, with the frame 310 holding the baffles 150 in theirretracted position of FIG. 8A, the baffles 150 may nonetheless be stowedwith the free ends 156 of the prongs 152 generally aligned with adirection of airflow. In other embodiments, the operator of the trailer120 might find it convenient to operate the trailer 120 with the baffles150 in a position having the prongs 152 forward-facing.

The foregoing examples of baffle retraction in FIGS. 7, 8 are depictedon a side surface of the trailer 120. They will be understood to beequally applicable to the opposing side surface and/or a top surface ofthe trailer 120 as well. Furthermore, the baffle 150 as described hereinwill be seen as equally applicable to other vehicles, or portionsthereon, including for example and without limitation the arrangement ofa baffle 150 or 250 as described herein to the tractor cab 110.

It will be appreciated that variants of the above-disclosed embodimentsand other features and functions, or alternatives thereof, may bedesirably combined into many other different systems or applications.Various presently unforeseen or unanticipated alternatives,modifications, variations, or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

What is claimed is:
 1. An aerodynamic drag reduction device, the devicecomprising a plurality of prongs arranged along a rear edge of a cargovehicle body, the plurality of prongs being resilient, the plurality ofprongs extending from a fixed end secured to the cargo vehicle bodyrearward in a flow-wise direction beyond the rear edge of the cargovehicle body to a free end, the plurality of prongs being disposed apartfrom each other, thereby enabling, under an influence of airflow overthe cargo vehicle body at a predetermined speed, deflection of the freeend above and below a first plane defined by a surface of the cargovehicle body to which the plurality of prongs is secured, the pluralityof prongs being resistant to deflection in a direction parallel to thefirst plane.
 2. The aerodynamic drag reduction device according to claim1, wherein a shaft of each prong comprises a perpendicularcross-section, a first neutral axis of the perpendicular cross-sectionbeing parallel to the first plane, an area moment of inertia of theperpendicular cross-section being a minimum around the first neutralaxis.
 3. The aerodynamic drag reduction device according to claim 1,wherein one of the plurality of prongs comprises a plurality of materialsections, each of the plurality of material section having a differentmodulus of elasticity.
 4. The aerodynamic drag reduction deviceaccording to claim 1, wherein one of the plurality of prongs comprises asubstantially uniform cross-section.
 5. The aerodynamic drag reductiondevice according to claim 1, wherein one of the plurality of prongscomprises a tapered cross-section.
 6. The aerodynamic drag reductiondevice according to claim 5, wherein one of the plurality of prongs istapered in its width.
 7. The aerodynamic drag reduction device accordingto claim 5, wherein one of the plurality of prongs is tapered in itsheight.
 8. The aerodynamic drag reduction device according to claim 1,wherein one of the plurality of prongs has radiused corners.
 9. Theaerodynamic drag reduction device according to claim 1, wherein one ofthe plurality of prongs comprises a vulcanized rubber material.
 10. Theaerodynamic drag reduction device according to claim 1, wherein one ofthe plurality of prongs is secured to the vehicle to enablerepositioning from a deployed position having the free end extendingbeyond the rear edge of the cargo vehicle body to a retracted positionhaving the free end nearer the rear edge of the cargo vehicle body. 11.The aerodynamic drag reduction device according to claim 10, wherein theaerodynamic drag reduction device is slideable in a flow-wise directionto reposition the plurality of prongs.
 12. The aerodynamic dragreduction device according to claim 10, wherein the aerodynamic dragreduction device is secured to a rotating frame member which isrotatable between the deployed position and the retracted position. 13.The aerodynamic drag reduction device according to claim 12, wherein thedevice is rotatable on the rotating frame member to maintain orientationof the plurality of prongs in a rearward extending direction.
 14. Theaerodynamic drag reduction device according to claim 12, wherein therotating frame member is securable with the plurality of prongs in thedeployed position.
 15. The aerodynamic drag reduction device accordingto claim 12, wherein the rotating frame member is securable with theplurality of prongs in the retracted position.
 16. The aerodynamic dragreduction device according to claim 1, in combination with anover-the-road cargo vehicle.
 17. The aerodynamic drag reduction deviceaccording to claim 15, wherein the cargo vehicle body comprises a rearface that is perpendicular to a direction of travel associated with thecargo vehicle body.
 18. An aerodynamic drag reduction device,comprising: a spine; a plurality of prongs, the plurality of prongsbeing resilient, each of the plurality of prong comprising a fixed endattached to the spine, an elongated shaft, and a free end opposing thefixed end on the elongated shaft, the plurality of prongs being disposedapart from each other, the plurality of prongs being flexible, therebyenabling, in response to airflow, deflection of the free end above andbelow a first plane defined by the spine, the plurality of prongs beingresistant to deflection in a direction parallel to the first plane. 19.A cargo vehicle comprising: a cargo area, the cargo area comprising arear surface perpendicular to a direction of travel; and an aerodynamicdrag reduction device affixed at a perimeter of the rear surface, theaerodynamic drag reduction device comprising a plurality of prongs, eachof the plurality of prongs having a fixed end attached to the cargovehicle, an elongated shaft, and a free end opposing the fixed end onthe elongated shaft, the fixed end extending rearward in a flow-wisedirection beyond the rear surface of the cargo area, the plurality ofprongs being disposed apart from each other, the plurality of prongsbeing flexible, thereby enabling, in response to airflow over the cargovehicle, deflection of the free end above and below a first planedefined by a surface of the cargo vehicle at the perimeter of the rearsurface, the plurality of prongs being resistant to deflection in adirection parallel to the first plane.
 20. The cargo vehicle accordingto claim 19, wherein the aerodynamic drag reduction device is secured tothe cargo vehicle to enable repositioning of the aerodynamic dragreduction device from a deployed position having the free end extendingbeyond the rear surface of the cargo area to a retracted position havingthe free end nearer the rear surface of the cargo area.